add generative word alignment model and primitive EM trainer. Model 1 and HMM are supported, without NULL source words

1 files changed, 113 insertions, 0 deletions

diff --git a/decoder/lexalign.cc b/decoder/lexalign.cc
new file mode 100644
index 00000000..ee3b5fe0
--- /dev/null
+++ b/decoder/lexalign.cc
@@ -0,0 +1,113 @@
+#include "lexalign.h"
+
+#include <iostream>
+
+#include "filelib.h"
+#include "hg.h"
+#include "tdict.h"
+#include "grammar.h"
+#include "sentence_metadata.h"
+
+using namespace std;
+
+struct LexicalAlignImpl {
+  LexicalAlignImpl(const boost::program_options::variables_map& conf) :
+      use_null(conf.count("lexcrf_use_null") > 0),
+      kXCAT(TD::Convert("X")*-1),
+      kNULL(TD::Convert("<eps>")),
+      kBINARY(new TRule("[X] ||| [X,1] [X,2] ||| [1] [2]")),
+      kGOAL_RULE(new TRule("[Goal] ||| [X,1] ||| [1]")) {
+  }
+
+  void BuildTrellis(const Lattice& lattice, const SentenceMetadata& smeta, Hypergraph* forest) {
+    const int e_len = smeta.GetTargetLength();
+    assert(e_len > 0);
+    const Lattice& target = smeta.GetReference();
+    const int f_len = lattice.size();
+    // hack to tell the feature function system how big the sentence pair is
+    const int f_start = (use_null ? -1 : 0);
+    int prev_node_id = -1;
+    for (int i = 0; i < e_len; ++i) {  // for each word in the *target*
+      const WordID& e_i = target[i][0].label;
+      Hypergraph::Node* node = forest->AddNode(kXCAT);
+      const int new_node_id = node->id_;
+      for (int j = f_start; j < f_len; ++j) { // for each word in the source
+        const WordID src_sym = (j < 0 ? kNULL : lattice[j][0].label);
+        TRulePtr& rule = LexRule(src_sym, e_i);
+        Hypergraph::Edge* edge = forest->AddEdge(rule, Hypergraph::TailNodeVector());
+        edge->i_ = j;
+        edge->j_ = j+1;
+        edge->prev_i_ = i;
+        edge->prev_j_ = i+1;
+        edge->feature_values_ += edge->rule_->GetFeatureValues();
+        forest->ConnectEdgeToHeadNode(edge->id_, new_node_id);
+      }
+      if (prev_node_id >= 0) {
+        const int comb_node_id = forest->AddNode(kXCAT)->id_;
+        Hypergraph::TailNodeVector tail(2, prev_node_id);
+        tail[1] = new_node_id;
+        Hypergraph::Edge* edge = forest->AddEdge(kBINARY, tail);
+        forest->ConnectEdgeToHeadNode(edge->id_, comb_node_id);
+        prev_node_id = comb_node_id;
+      } else {
+        prev_node_id = new_node_id;
+      }
+    }
+    Hypergraph::TailNodeVector tail(1, forest->nodes_.size() - 1);
+    Hypergraph::Node* goal = forest->AddNode(TD::Convert("Goal")*-1);
+    Hypergraph::Edge* hg_edge = forest->AddEdge(kGOAL_RULE, tail);
+    forest->ConnectEdgeToHeadNode(hg_edge, goal);
+  }
+
+  inline int LexFeatureId(const WordID& f, const WordID& e) {
+    map<int, int>& e2fid = f2e2fid[f];
+    map<int, int>::iterator it = e2fid.find(e);
+    if (it != e2fid.end())
+      return it->second;
+    int& fid = e2fid[e];
+    if (f == 0) {
+      fid = FD::Convert("Lx_<eps>_" + FD::Escape(TD::Convert(e)));
+    } else {
+      fid = FD::Convert("Lx_" + FD::Escape(TD::Convert(f)) + "_" + FD::Escape(TD::Convert(e)));
+    }
+    return fid;
+  }
+
+  inline TRulePtr& LexRule(const WordID& f, const WordID& e) {
+    map<int, TRulePtr>& e2rule = f2e2rule[f];
+    map<int, TRulePtr>::iterator it = e2rule.find(e);
+    if (it != e2rule.end())
+      return it->second;
+    TRulePtr& tr = e2rule[e];
+    tr.reset(TRule::CreateLexicalRule(f, e));
+    tr->scores_.set_value(LexFeatureId(f, e), 1.0);
+    return tr;
+  }
+
+ private:
+  const bool use_null;
+  const WordID kXCAT;
+  const WordID kNULL;
+  const TRulePtr kBINARY;
+  const TRulePtr kGOAL_RULE;
+  map<int, map<int, TRulePtr> > f2e2rule;
+  map<int, map<int, int> > f2e2fid;
+  GrammarPtr grammar;
+};
+
+LexicalAlign::LexicalAlign(const boost::program_options::variables_map& conf) :
+  pimpl_(new LexicalAlignImpl(conf)) {}
+
+bool LexicalAlign::Translate(const string& input,
+                      SentenceMetadata* smeta,
+                      const vector<double>& weights,
+                      Hypergraph* forest) {
+  Lattice lattice;
+  LatticeTools::ConvertTextToLattice(input, &lattice);
+  smeta->SetSourceLength(lattice.size());
+  pimpl_->BuildTrellis(lattice, *smeta, forest);
+  forest->is_linear_chain_ = true;
+  forest->Reweight(weights);
+  return true;
+}
+